Semiconductor photo-detecting element

Abstract

In a semiconductor photo-detecting element (an avalanche photodiode), a high-sensitivity element is obtained by incorporating a multiplication layer having high-performance multiplication characteristics. By using a structure which reduces an electric field applied to an etching stopper layer, it is possible to use a multiplication layer having higher-performance multiplication characteristics (a multiplication layer which performs multiplication with a high electric field). The first method to realize this is to use a conductivity type multiplication layer. The second method is to use a structure in which a field buffer layer of the second conductivity type is incorporated. As a result of the use of these methods, a structure which applies an electric field lower than the multiplier electrical field to the etching stopper layer is obtained.

1. A semiconductor photo-detecting element, comprising:
 a semiconductor substrate; 
 a buffer layer of a first conductivity type on the semiconductor substrate; 
 a light-absorbing layer on the buffer layer; 
 a field buffer layer of the first conductivity type on the light absorbing layer; 
 a multiplication layer on the field buffer layer; 
 an etching stopper layer on the multiplication layer; 
 a buffer layer of a second conductivity type on the etching stopper layer; and 
 a contact layer of the second conductivity type on a the buffer layer, wherein 
 a first field strength applied to the etching stopper layer, measured in a depth direction running through each of the layers, is lower than a second field strength applied to the multiplication layer as measured in the depth direction. 
 
     
     
       2. The semiconductor photo-detecting element according to  claim 1 , wherein an impurity of the light-absorbing layer is the first conductivity type. 
     
     
       3. The semiconductor photo-detecting element according to  claim 1 , wherein an impurity of the light-absorbing layer is the second conductivity type. 
     
     
       4. The semiconductor photo-detecting element according to  claim 1 , wherein,
 a breakdown electrical field strength of the etching stopper layer is lower than a breakdown electrical field strength of the multiplication layer, and 
 the first field strength applied to the etching stopper layer is lower than the breakdown electrical field strength of the etching stopper layer. 
 
     
     
       5. The semiconductor photo-detecting element according to  claim 1 , wherein,
 a breakdown electrical field strength of the etching stopper layer is lower than a breakdown electrical field strength of the multiplication layer, and 
 the second field strength applied to the multiplication layer is higher than the breakdown electrical field strength of the etching stopper layer. 
 
     
     
       6. The semiconductor photo-detecting element according to  claim 1 , further comprising:
 a second field buffer layer of the second conductivity type between the multiplication layer and the etching layer configured to relax the field of the multiplication layer. 
 
     
     
       7. The semiconductor photo-detecting element according to  claim 6 , wherein
 an impurity of the multiplication layer is of the first conductivity type. 
 
     
     
       8. The semiconductor photo-detecting element according to  claim 6 , wherein
 an impurity of the multiplication layer is the second conductivity type. 
 
     
     
       9. The semiconductor photo-detecting element according to  claim 6 , wherein,
 the layer thickness (dm(cm)) of the field buffer layer of the second conductivity type, the impurity concentration of the second conductivity type (Ndk (cm −3 )) of the field buffer layer, and the magnitude of an electric field (ΔEk (kV/cm)) satisfy the relationship Ndk≧k×eO×ΔEk/(q×dk) (where k is the dielectric constant of the field buffer layer, eO is the permittivity in a vacuum, and q is the elementary quantity of electric discharge), and 
 the electric field relaxes the second field strength applied to the multiplication layer. 
 
     
     
       10. The semiconductor photo-detecting element according to  claim 1 , wherein an impurity of the multiplication layer is of the second conductivity type and has an impurity concentration of not less than 1×10 16  (cm −3 ). 
     
     
       11. The semiconductor photo-detecting element according to  claim 1 , wherein the multiplication layer is a single layer in which the ratio of elements forming the multiplication layer is constant. 
     
     
       12. The semiconductor photo-detecting element according to  claim 11 , wherein the multiplication layer is a layer formed from InAlAs. 
     
     
       13. The semiconductor photo-detecting element according to  claim 12 , wherein the etching stopper layer is a layer formed from InP or In x Ga (1-x) As y P (1-y)  (0≦x≦1.0, 0≦y ≦1.0). 
     
     
       14. The semiconductor photo-detecting element according to  claim 11 , wherein the multiplication layer has a thickness of not more than 0.3 μim. 
     
     
       15. The semiconductor photo-detecting element according to  claim 1 , wherein,
 the layer thickness (dm(cm)) of the multiplication layer, the impurity concentration of the second conductivity type (Ndm (cm −3 )) of the multiplication layer, and the magnitude of an electric field (ΔEm (kV/cm)) satisfy the relationship Ndm ≧k×eO×ΔEm/(q×dm) (where k is the dielectric constant of the multiplication layer, eO is the permittivity in a vacuum, and q is the elementary quantity of electric discharge), and 
 the electric field relaxes the second field strength app lied to the multiplication layer. 
 
     
     
       16. The semiconductor photo-detecting element according to  claim 1 , wherein the first field strength is lower at any portion of the etching stopper layer than the second field strength. 
     
     
       17. The semiconductor photo-detecting element according to  claim 1 , wherein the multiplication layer reduces an electric field applied to the etching stopper layer such that the first field strength applied to the etching stopper layer is lower than the breakdown electrical field strength of the etching stopper layer.